MOTION ESTIMATION ALGORITHM

摘要

A method for identifying an optimum motion vector for a current block of pixels in a current picture in a process for performing motion estimation. The method is implemented by evaluating a plurality of motion vector candidates for the current block of pixels by, for each motion vector candidate, and calculating an error value that is representative of the differences between the values of the pixels of the current block of pixels and the values of a corresponding number of pixels in a reference block of pixels. While evaluating each motion vector candidate, the error value is checked, preferably at several points, while calculating the error value, and the evaluation is aborted for that motion vector candidate upon determining that the error value for that motion vector candidate exceeds a prescribed threshold value. The motion vector candidate that has the lowest calculated error value is selected as the optimum motion vector for the current block of pixels. The motion vector candidates are preferably evaluated in two distinct phases, including a first phase that includes evaluating a subset of the motion vector candidates that have an intrinsically high probability of being the optimum motion vector candidate, and a second phase that includes performing a spatial search within a prescribed search region of a reference picture in order to identify a different reference block of pixels within the prescribed search region for each respective motion vector candidate evaluation. The subset of motion vector candidates preferably includes a first motion vector candidate that corresponds to a location of the reference block of pixels in a reference picture that is the same as the location of the current block of pixels in the current picture, a second motion vector candidate that corresponds to a location of the reference block of pixels in a previous picture that is the same as the location of the current block of pixels in the current picture, and a third motion vector candidate that constitutes an optimum motion vector previously determined for a preceding block of pixels in the current picture. Preferably, no further evaluations are performed if it is determined that the error value for the first motion vector candidate is below a prescribed motion estimation termination threshold value. The method is executed by software that operates a software-implemented state machine. The software preferably includes source code that defines a search sequence, and a function that builds the state machine in a prescribed memory space.